How to troubleshooting issues with monitors or displays not powering on.
Check that the power cable is properly plugged in
Try using the buttons on the display to power these on. They are usually located on the edge of the bezel or just behind the monitor bezel. Some newer LGs and Samsungs only have a single joystick style button.
If there is a room control panel, make sure the system is turned on.
If there is a room control panel, try restarting the system